This invention relates to method and arrangements for representing data in vehicle navigation systems.
Navigation systems for vehicles are arranged so that map information stored in a memory of large capacity, for example a CD-ROM, is indicated and/or reproduced on a picture screen. The map information may be displayed, for example in the form of routes, i.e. by direction and/or course of travel, by means, distances and directions of roads, places along the roads or in the form of places and names of intersections and localities, and names of buildings.
The purpose of such navigation systems is to indicate to the vehicle operator on the screen, the place where the vehicle is located, the vehicle position being indicated in each instance with a map image as a background. The indication of the vehicle position with a map image in the background may be achieved in several ways. In one display method the vehicle indicator is fixed in one position, generally a central position, relative to the screen and the background image of the map is shifted appropriately as the vehicle travels.
This method is classified in turn into two submethods:
(a) The upper direction of the screen is fixed, always oriented, for example, to the north. The background map image shifts parallel to the direction of a mark or icon representing the vehicle. Although the mark remains in one position on the screen, it changes its orientation on the screen in accordance with the actual direction of motion or travel of the vehicle with respect to the map, and the background map image shifts its direction of motion in accordance with the change of orientation of the mark.
(b) The mark does not change its orientation in accordance with a change of direction of motion of the vehicle. However, the background image of the map moves parallel to the orientation of the mark and thus rotates in accordance with the actual motion of the vehicle with respect to the ground.
According to a second basic method, a single image section of the map is reproduced in stationary form and the top to the map on the screen is fixedly directed to the north. The mark representing the vehicle moves over the stationary image of the map until the vehicle reaches a location corresponding to a marginal section of the map image on the screen. At that time, and successively thereafter, additional, non-shifting sections of the map are displayed to show the region in which the vehicle is traveling.
In another navigation system, after entry of a destination, the route from the present location to the destination as recommended by the system is automatically selected on the screen and indicated on the map. This navigation system, indicating a combination of both the route and the present vehicle position, in principle displays on the screen only the route along which the vehicle is traveling. At best, it will show corners at which the vehicle can turn. Therefore, such a navigation system has the following disadvantages. In the display on the screen, the length of the remaining route shortens as the vehicle position travels along the route. Also, the end of the screen may possibly be reached before the vehicle arrives as the destination. At that time, the continuation of the route is not shown, and the operator is not able to ascertain the present vehicle position. If, according to the method described above, the position of the vehicle indicator is maintained at the center of the screen, the length of the route reproduced in the display amounts to about half the total size of the screen. This is disadvantageous in terms in terms of effective use of a small or narrow screen.
U.S. Pat. No. 5,274,387 discloses a navigation system for vehicles with a display predetermined size to reproduce a map image having provision for setting the scale of the map image and for showing the present vehicle position in which, in a first mode, the map image is reproduced to a scale and shifted so that the current vehicle position is always shown at about the center of the display, whereas, in a second mode, the route of travel is indicated at essentially its maximum length on the map image. In the second mode, before the commencement of display, a map image is set on the display permitting selection of a maximal segment of the route of travel for display and thereafter the indicated segment of the travel route is traversed at constant map scale so that, after traversal of the displayed segment of the travel route, another map image is displayed having the same scale and again displaying a maximal segment of the travel route.
U.S. Pat. No. 5,537,323 discloses a navigation system having a memory for storing cartographic data, a vehicle position detector unit, a control unit, an input unit, an image memory and a display unit, the control unit being arranged to direct a user along a previously determined route on the basis of data contained in the vehicle position detector unit and the cartographic data. The control unit is also arranged to successively reproduce the relevant map sections on the display unit from cartographic data stored in the image memory and selected in terms of a current vehicle position determined by the position detector unit. The control unit includes an image processor for reproducing the previously determined route in a complete manner in the map section of the display unit, while the image processor represents the route segment traversed to reach the current vehicle position in a different manner, reproducing only the local surroundings of the current vehicle position, including local intersections and route indications on the map.
German Offenlegungsschrift No. 195 16 647 discloses a navigation system for motor vehicles having a data memory and a display supported with information from the memory for a map section containing the current vehicle location, in which the scale of the map section is automatically enlarged at a low vehicle section. The automatic enlargement of the scale saves trouble for the operator. Moreover, coupling of the map scale with the vehicle speed assures that the operator actually receives the map section and scale he requires in terms of his style of driving. At high speed, as for example on a motorway, the map is reproduced at a small scale and contains information about a comparatively large area.
Typically, a small scale of 1:100,000 may be used in this case. At low speeds, however, such as occur in city traffic, the map scale is enlarged to a scale of 1:10,000 for example. Also, an intermediate scale of 1:50,000, for example, may be provided when the vehicle is at an intermediate speed. The assignment of a scale to the current vehicle speed may reasonably be made according to an average value of the vehicle speed. For example, the average vehicle speed may be taken over a period of 10 minutes. In addition, according to this reference the change of scale may also be made dependent on the distance of the vehicle from its destination.
A destination in turn may, for example, be entered before the beginning of the trip or else entered for a selected trip distance. For example, if the vehicle is at a distance of 1 kilometer from its destination, a switch to the larger scale may be made automatically. This facilitates convenient finding of the destination. A disadvantage of such navigation systems is that the required density of information does not automatically depend on the vehicle speed, so that the vehicle operator may receive too much or too little information at the scale shown.